Favorite reverse bias protection for battery circuits
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From: Charlie E. on 16 Mar 2010 13:56 Hi All, Still working on my color reader, and getting close. Biggest problem is that now I have almost TOO much drive on my LEDs, but that I can deal with! Now, to the latest problem. My system is for the visually impaired. I just put the batteries in one of my prototypes backwards, and it didn't last very long. While I expect this device to have very long battery life, since it normally doesn't operate but for a second or two, it looks like the MC1253's don't like getting reversed biased very long. So, for my design question of the day - What is your favorite circuit for preventing reverse bias from the batteries? The old diode trick drops too much voltage, so wondered if there are any clever FET tricks to block backwards voltages. Thanks! Charlie
From: BillyGates on 16 Mar 2010 14:02 Charlie E. wrote: > Hi All, > Still working on my color reader, and getting close. Biggest problem > is that now I have almost TOO much drive on my LEDs, but that I can > deal with! > > Now, to the latest problem. My system is for the visually impaired. I > just put the batteries in one of my prototypes backwards, and it > didn't last very long. While I expect this device to have very long > battery life, since it normally doesn't operate but for a second or > two, it looks like the MC1253's don't like getting reversed biased > very long. So, for my design question of the day - What is your > favorite circuit for preventing reverse bias from the batteries? The > old diode trick drops too much voltage, so wondered if there are any > clever FET tricks to block backwards voltages. > > Thanks! > > Charlie Yes, there are fet "tricks" that when reverse biased bias the fet to turn it off. It is essentially an "active diode".
From: Hammy on 16 Mar 2010 14:03 On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> wrote: >Hi All, >Still working on my color reader, and getting close. Biggest problem >is that now I have almost TOO much drive on my LEDs, but that I can >deal with! > >Now, to the latest problem. My system is for the visually impaired. I >just put the batteries in one of my prototypes backwards, and it >didn't last very long. While I expect this device to have very long >battery life, since it normally doesn't operate but for a second or >two, it looks like the MC1253's don't like getting reversed biased >very long. So, for my design question of the day - What is your >favorite circuit for preventing reverse bias from the batteries? The >old diode trick drops too much voltage, so wondered if there are any >clever FET tricks to block backwards voltages. > >Thanks! > >Charlie I usually use #2 on this page a shorting shottky. http://www.recom-international.com/press/Reverse%20Polarity%20Protection%20for%20DC/DC%20Converters.html
From: Rich Webb on 16 Mar 2010 14:12 On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> wrote: >Hi All, >Still working on my color reader, and getting close. Biggest problem >is that now I have almost TOO much drive on my LEDs, but that I can >deal with! > >Now, to the latest problem. My system is for the visually impaired. I >just put the batteries in one of my prototypes backwards, and it >didn't last very long. While I expect this device to have very long >battery life, since it normally doesn't operate but for a second or >two, it looks like the MC1253's don't like getting reversed biased >very long. So, for my design question of the day - What is your >favorite circuit for preventing reverse bias from the batteries? The >old diode trick drops too much voltage, so wondered if there are any >clever FET tricks to block backwards voltages. This http://www.maxim-ic.com/app-notes/index.mvp/id/636 Maxim appnote describes the pros and cons of several standard approaches. -- Rich Webb Norfolk, VA
From: Joerg on 16 Mar 2010 14:18
Hammy wrote: > On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> > wrote: > >> Hi All, >> Still working on my color reader, and getting close. Biggest problem >> is that now I have almost TOO much drive on my LEDs, but that I can >> deal with! >> >> Now, to the latest problem. My system is for the visually impaired. I >> just put the batteries in one of my prototypes backwards, and it >> didn't last very long. While I expect this device to have very long >> battery life, since it normally doesn't operate but for a second or >> two, it looks like the MC1253's don't like getting reversed biased >> very long. So, for my design question of the day - What is your >> favorite circuit for preventing reverse bias from the batteries? The >> old diode trick drops too much voltage, so wondered if there are any >> clever FET tricks to block backwards voltages. >> >> Thanks! >> >> Charlie > I usually use #2 on this page a shorting shottky. > > http://www.recom-international.com/press/Reverse%20Polarity%20Protection%20for%20DC/DC%20Converters.html That renders the unit dead and a blind or almost blind person will have a hard time finding or buying the proper fuse and installing it. Charlie: Solution #3 is the ticket (look on Hammy's link). But make sure that the FET is guaranteed to be fully turned on at the lowest allowed battery voltage, IOW the point where an UVLO comes on. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |